In an internal combustion engine, the concept of "stroke" is directly tied to the function of the crankshaft. While "stroke crank" isn't a standard technical term, the stroke length of an engine cylinder is determined by the crankshaft.
Understanding Engine Stroke
The engine's stroke refers to a specific measurement within the cylinder. According to the provided reference:
- An engine's stroke is the distance the piston travels inside the cylinder.
- This distance is the full travel from the top of its motion (Top Dead Center or TDC) to the bottom of its motion (Bottom Dead Center or BDC).
- Stroke length can be listed in either inches or millimeters, depending on the engine specifications.
The Role of the Crankshaft
The crankshaft is a crucial component in an engine. It converts the linear (up and down) motion of the pistons into rotational motion, which is then used to power a vehicle or other machinery.
The reference states that Stroke length is determined by the crankshaft. This is because the design of the crankshaft dictates how far the piston can move.
How the Crankshaft Determines Stroke
The crankshaft has offset sections called crankpins or throws where the connecting rods attach. The distance from the center axis of the crankshaft to the center axis of the crankpin is known as the crank radius or throw radius.
The piston travels downwards as the crankshaft rotates half a turn, pulling the piston from TDC to BDC. It travels upwards the next half turn, pushing the piston from BDC to TDC. The total distance the piston travels (the stroke) is exactly twice the distance of the crank radius (the throw).
Key Relationship:
- Stroke Length = 2 × Crank Radius (Throw)
This means engineers can design engines with different stroke lengths simply by changing the amount of offset built into the crankshaft throws.
Stroke vs. Bore
Engine dimensions are often described by their bore (the diameter of the cylinder) and their stroke (the piston travel distance determined by the crankshaft). The ratio between bore and stroke significantly impacts an engine's characteristics, such as its power delivery and torque curve.
| Component | Definition | Determined By... |
|---|---|---|
| Stroke | Distance piston travels inside the cylinder | Crankshaft design |
| Bore | Diameter of the cylinder | Cylinder block design |
In essence, while "stroke crank" isn't a recognized part, the crankshaft is the fundamental component that defines and controls the stroke length in an engine.
